Why do koalas spend most of their time sleeping?
Koalas have a slow metabolic rate which is required for them to
digest the eucalyptus leaves on which they feed.
Eucalyptus leaves are very fibrous and rather low in nutrition,
so the fact that the koala has a slow metabolic rate means it can
keep the food within its digestive system for as long as possible
in order to maximise the energy that can be extracted from the
leaves. This slow metabolic rate also means the koalas sleep for
more time each day in order to conserve energy.